Axial flow compressors



Jan. 2l, 1958 A. .1. PENN ETAL 2,820,588

v AXIAL FLOW coMPREssoRs Filed nec. 11, 1955 `2 sheets-sheet 1 f Jl 110 FITTORNEXS Jan. 21, 1958 A. J. PENN ET AL 2,820,588

Axium FLOW coMPREssoRs 2 Sheets-Sheet 2 Filed Dec. ll, 1953 NVE/waas @www United States Patent AXIAL FLow coMrREssoRs Alfred John Penn, Northwood, and Leslie Alan Nevard, Liverpool, England, assignors to D. Napier & Son Limited, London, England, a British company Application December 11, 1953, Serial No. 397,728

Claims priority, application Great Britain December 15, 1952 Claims. (Cl. 230-114) This invention relates to multi-stage axial flow compressors such as are used, for instance, for compressing the working medium in gas turbine plants.

It is an object of the present invention to provide a multi-stage axial ow compressor which will facilitate starting and acceleration and which has an improved part-load performance.

In a multi-stage axial liow compressor according to the present invention, a part of the rotor which carries blades of the earlier stages is mounted so that it is capable of rotating independently ofanother part of the rotor which carries blades of the later stages and to which the drive is imparted, and a disengageable coupling is provided for connecting the rotor parts together.

The reason why this arrangement can facilitate starting and acceleration is as follows. A compressor rotor has a large inertia, and it must be run up to quite a high speed before the plant becomes self-sustaining, that is to say, when the turbine is producing suicient power to drive the compressor without external aid. It is therefore necessary for the starting motor to impart a large amount of energy to the rotor. In the present invention, by disengaging the coupling for starting, the inertia of the rotor is reduced in that the starting motor only has to accelerate the part of the rotor which carries the blades of the later stages. When the plant has become self-sustaining, or when the turbine is producing enough power to reduce the load on the starting motor, the coupling can be engaged so that the part of the rotor which carries the blades of the earlier stages will be speeded up to the same speed as the positively driven part and the two parts will then rotate as one. Thereafter the compressor will act in the same way as an axial flow compressor of orthodox construction. When the coupling is disengaged, the blades of the earlier stages will otter only slight resistance to the tlow of working medium induced by the later stages, so that the only adverse effect which the earlier stages have is to produce a slight pressure drop in the working medium which transverses them.

As indicated above, the advantages of the invention are not confined to the improvement in starting and acceleration, since an improved part-load performance is also obtainable.

In a gas turbine plant it would be desirable for the pressure-mass flow characteristic of the compressor to match that of the turbine over the whole range of mass ow. Unfortunately, the characteristics of conventional axial ilow compressors and turbines are such that, if they are properly matched for normal full-load conditions, they are not properly matched at part-load, with the result that the compressor operation may become unstable. One way of dealing with the problem is to vary the compressor characteristic by providing it with adjustable guide vanes. However, such vanes may not be sufciently effective at medium or small mass ows, with vthe result that medium or low load running is apt to be unstable.

By the present invention, at medium or low loads, the

2,820,588 v Patented Jan. 21, 1958 ICC earlier stages can be rendered inoperative so that, in eect, the compressor is converted into one of fewer stages, with a better surge characteristic in the medium and lower part of the mass llow range. When the mass flow has increased to an appropriate value, the rst stages may be brought into operation by engaging the coupling, thereby converting the compressor, in effect, to one of conventional type.

The coupling together of the compressor parts at the desired speed may be eected automatically, for instance by a centrifugal coupling adapted to couple the two parts together at a predetermined rotational speed.

In one form `of the invention adjustable guide vanes are provided for operation in the intermediate ranges. This has the advantage that it enables the coupling to be engaged at a lower speed than would be the case if no such vanes were provided.

A second disengageable coupling may be provided between a stationary part of the compressor and the part of the rotor which carries the blades of the earlier stages, so that this part of the rotor can be held stationary when the first-mentioned coupling is disengaged. Then at an appropriate speed, the second coupling can be disengaged and the first-mentioned coupling engaged, so that the part of the rotor carrying the blades of the earlier stages is rapidly accelerated from rest until it is rotating at the same speed as the second part of the rotor. If desired there may be a delay between the disengagement of the second coupling and the engagement of the first coupling, to permit the initial acceleration of the part of the rotor carrying the blades of the earlier stages to be accomplished by the windmill eect of the air dow through these blades.

As an alternative to holding stationary the part of the rotor which carries the blades of the earlier stages, this part can be permitted to windmill at low mass ows, in which case the second coupling may be dispensed with.

Where two disengageable couplings are provided, these may be combined in a single mechanism, i. e. mechanism in which at least one part is common to both couplings.

The invention may be performed in various ways, and one particular embodiment and a modification thereof will be specifically described by way of example with reference to the accompanying drawings, in which:

Figure l is a side elevation of the axial llow compressor which is partially cut away and sectioned to show the internal arrangements;

Figure 2 shows a part of the mechanism of Figure l on a larger scale;

Figure 3 shows another form of mechanism which is alternative to that shown in Figure 2; and

Figure 4 is a family of curves illustrating the perform ance of the compressor.

The axial ow compressor shown in Figure l is intended for supplying compressed air to a turbine (not shown) via a combustion chamber (not shown). In the compressor there is a cylindrical casing 10 which carries several rings of xed stator blades 11 and two rings 1 2 and 13 of angularly adjustable guide vanes. Running through the centre of the compressor is a shaft 14 on which are xed several rotor blade rings 15 which comprise the later stages of the compressor. Mounted on the shaft 14 so as to be freely rotatable thereon is a sleeve 16 on which are mounted several rotor blade rings 17 which comprise the earlier stages of the compressor. The sleeve 16 can be clutched to the shaft 14 by a disengageable coupling 18. Alternatively, it can be locked to a stationary part of the compressor by another disengageable coupling 19. The couplings 18 and 19 are shown more detail in Figure 2.

lDealing rst with the coupling 18; this comprises two cone discs 20 and 21 which are splined to the shaft 14 and are `urged togetherby -springs'ZZ'and 23.'V jSealing anges Ztl-and 2S, which can slide over each other, are provided near the peripheries of the cone discs 20 and 21 respectively. Mounted o n the end of the sleeve 16 is an :annular `channel 26 of trough-shaped' cross-'sectiomthe mchnationfofits Isides beingthe same as Ythe ,inclinations of the kcone surfaces of thediscs' 20 and To the space Vbetween the discs `20 and 2'1'which is bounded ion its `outer periphery by `the sealing-flanges 24 and' '2 5,l a duid under pressure (e. g. oil or air) can be admittedV from the hollow-centre of the Vshaft 14 through a lpassage l2'7. For automatic operation, this uid pressure'may )be a 'functionof the speed-ofrotation, for Yinstance airfat the delivery'pressurefof-thecompressoror oil `sunplied'by a centrifugal-pump, suchy asV speed'.responsive-#uidpressure source S as shown in Figure l'. :When `lluidnitriet-pressure is so admitted, -thecone discs 20 and 271 are'fforced apart against the action of springs 22-and 23 Aso thattheir cone surfaces-engage tthe -walls of lthe :channel 26 and thus lock the sleeve Y116 'tothe shaft 14; Conversely, when-the pressure is released, the springs 2 2-fand23 force the cone discs 20 and v21 out ofengagementwith the trough member 26 so that-the sleeve 16-is free'dfrom'the shaft 14 in the rotational sense.

Turningnow to theVv coupling 19; v-there `is keyed'to the vshaft 16 a drum 28. Mounted within the drum 28 on -xed pins 29 are arcuate friction shoes l30 which, by means-of an-expanding mechanism y(not shown), can be forced Youtwardlyto engage the 'drum 28 and thus hold thisV drum stationary, and with 'itvthe sleeve 4v16. Y

In the arrangement "show-n in :Figures *l Land 2, the disengageable couplings 18 and "are actuated independentlyrby -suita'blecontrol-mechanisms and can `be brought into operation as and when required to Vsuit the runningeonditions. Howeven'fitds possible nto substitute for the disengageablecoupling 18 shown in 'Figures l and 2Y an automatic clutch mechanism whichcomesinto operal vtion to lock lthe Ysleeve 16 vto the l shaft 14jwhen'the rotational yspeed of the latter has risen gto a'certain value. Figure 3 shows -suchfa mechanism. In this mechanism y the end of the sleeve v16v'carries an annular channel`g31 of shaft 14. These weights have inclined anks 35, the

angle .of which is the same as Ythe angle Yof the Atroughshaped annular channel 31. As the shaft '14 rotates, Vthese weights y outwards and engage the walls of the channel 31. As the speed of rotation "of the shaft 1'4 increases, the centrifugal force exerted by these weights also increases until the frictional force which they Y,exertV on the channel 31 exceeds vthe resistance Ito movement "of `the Vsleeve 16, whereupon vthis sleeve begins to rotate.

At normal running speeds, the centrifugal Yforce exerted by the weights 34 is so great that there `is no slip between fthemandthe walls of the `channel 31.

This mechanism also includes a somewhat different of l-disengagealzvle coupling Vcorresponding to the `coupling 19 of Figure 2.

In this case the -drum 2-8 of Figure 2 is replaced by -an annulus 36 `having a Vfriction -surface37 which can engage the outer surface of the annular channel 31. Normally this-annulus is held inthe "oi positionl by a spring 38. T o the left of the annulus 3 6thereis Aan annular `face-cam V39 having-ramp surfaces lCo-operating with these ramp surfaces are fixed n Vfp'vlfoject'ions*41, -so that-ifthe face-cam -is rotated, the ramp jsufaces^40 will `ride lup 'on the projections 41, thereby f'movingthe annulus'36 into frictional engagement V`with hef-outer surface of the channel member V31 and holding "thcsleeve'lt stationary. in thistarrangementboth the couplingsv are combined in a single mechanismin Ythat ,part x'is common to both.

4 For starting the compressor the following procedure is followed. First, the sleeve 16 is held stationary by Yengaging the disengageable .coupling 19 (expanding the shoes 30 against the drum 28 in Figure 2, or advancing the annulus 36 to the right to engage the channel 31 in Figure 3). Next, the shaftlidis run up to speed by a starter motor (not shown). Since thesleeve 16 and the blades 17 which it carries are not rotated Aby the starter Vmotor the load on .this motor -sless than it would be if it gageable coupling may Vnow be disengaged so that thesleeve 16 is free Vto rotate. 'The rush of air through theV blades 17 starts to rotate the sleeve16; in other Words it begins to windmill. When the sleeve is rotating fast enough fit can be clutched fto the shaft 14 so that Ythe whole rotor rotates as one. In Figure 2-this clutching-in is .done by applying fluid pressure between the cone discs 20 `and 21such as fromspeedresponsive iluid pressure source yS so-that they grip the channel 26, while in Figure 3 the design is such that the frictional forcebetweenthe weights 34 and the channel 31 at the appropriate rotational speed `of the shaft 14 overcomes the drag of the Sleen/e116. In `both casesfthe `frictional drag of this disenga-geable coupling may fbe used to augment or to supplant the windmillet`fect in'running the sleeve 16 upto speed. t l

The advantages of vthe-inventionfor part-loadoperation yare illustrated in Figure 4, which is a-curve of-pressure 'ratio (R) plotted against mass flow through the cornprevssorlW). The curve T is the turbine load line, that is tosay, ,it represents the mass #dow ofsair demanded b'y the' turbine -at different pressures vfor a constant load.

The curve C1 represents Vthe maximum compressor Iperformance with only the'later stages running, while' the curve C2 represents the maximum compressor performance with all stages'in opera-tion.

Assuming now that the compressor is running with only the later stages'working,i. e. on the line C1. It is clear from Figure 4 that the compressor can supply the vturbine adequately on Athis line, 'but that at high speeds the pressure ratio corresponding to ltherdcsire'd mass flow 'is high, and consequently the compressor will absorb a lot -load line T, y'sogthat Tat these speeds the output of the compressor-is inadequate. Consequently, it 'is' desirable lto workon the'line C, up to the point x, say, and then change vrovente-the lineCz at the pointk y. It will 'be 'o'bservedvthat, sincetherchange-ovcr koccurs at a definite speed, both the points, x and y lie on the sa-me speed line,

-In order to reduce the compression yWork still further, the compressor couldbe run up to a Alower speed on '-th'elne C1, say 'to fthe point-z, and then from 2 to y the adjustment of the delivery could be effected by suitably adjusting therguide vanes 12 and 13.

What we claim as our invention and desire to secure by 'Letters Patent ist'` e l. A multi-stage axial Silow compressor for compressing a gaseous medium comprising a irst rotor part, blades Jrfor the `rst compression part mounted `on said first yrotor part, a second rotorpart, driving means for imparting rotation to said `second-rotor part, means supporting 'said first rotor part lfor rotation 'independently of .said secondl rotor part and said driving means, blades. forthe flater compression ystages mounted on `saicl second rotor part, passage means whichfconvey all the gaseous medium passed throughsaid iirst compression part lto-saidlatercompression `stages, disengageablt. coupling means bc tween said second rotor part and said rst rotor part which, when engaged, couple the said rotor parts for rotation together at the same speed, and speed responsive means for engaging said coupling means when said later stage attains a predetermined speed whereby Windmilling of said first compression part is stopped and said rst compression part is driven with the later stages.

2. A multi-stage axial flow compressor according to claim 1 in which said disengageable coupling means comprises a frictional coupling means having friction mem bers, said speed responsive means including means for moving said friction members into engagement on the application of fluid pressure to one of said members, means admitting fluid pressure to said last-mentioned member, and means for regulating said fluid pressure as a function of the speed of rotation of said driving means.

3. A multi-stage axial ow compressor according to claim l in which said disengageable coupling means is a centrifugal coupling adapted to couple said rst rotor part to said second rotor part automatically when said second rotor part is rotated above a predetermined speed.

4. A multi-stage axial flow compressor comprising a rst rotor part, blades for the earliest compression stages mounted on said rst rotor part, a second rotor part, driving means for imparting rotation to said second rotor part, means supporting said first rotor part for rotation independently of said second rotor part and said driving means, blades for the later compression stages mounted on said second rotor part, and disengageable coupling means between said second rotor part and said first rotor part which, when engaged, couple the said rotor parts for rotation together and a stationary part and disengageable coupling means between said rst rotor part and said stationary part.

5. A multi-stage axial ow compressor according to claim 4 in which there is at least one member which is common to both said disengageable coupling means.

References Cited in the ile of this patent UNlTED STATES PATENTS 2,321,276 De Bolt June 8, 1943 2,613,029 Wilde Oct. 7, 1952Y 2,672,726 Wolf et al. Mar. 23, 1954 FOREIGN PATENTS 611,447 Great Britain Oct. 29, 1948 

